Method and system for engine knock detection

ABSTRACT

Methods and systems are disclosed for operating an engine that includes a knock control system. The method and system may increase opportunities to learn one or more engine knock background noise levels via changing poppet valve timing and/or fuel injection timing. The method and system may also improve knock detection if knock sensor degradation is suspected.

FIELD

The present application relates to methods and systems for learningengine knock background noise levels.

BACKGROUND/SUMMARY

An engine may include an engine knock control system to increase engineefficiency and reduce the possibility of engine degradation. The knockcontrol system may include a knock sensor that senses vibrations of theengine's block. The knock control system may observe particularfrequencies output from the knock sensor to determine the presence orabsence of engine knock. Engine knock or detonation may occur when endgases within the cylinder ignite before a flame front generated by aspark ignites the end gases during a cycle of a cylinder. The ignitionof the end gases due to higher cylinder temperatures and pressures maystimulate vibration within the engine's block, which may be detected viathe knock sensor. The knock system may determine that engine knock ispresent based on output of the knock sensor during a crankshaft intervalwhere knock may be expected and an engine knock background noise level.The engine knock background noise level may reflect engine vibrationwhen engine knock is not present. However, if the knock sensor degradesor if engine knock background noise level changes or varies from engineto engine, engine knock may not be observed by the control system or itmay be falsely indicated by the control system. Therefore, it may bedesirable to provide a way of operating the knock control system suchthat the possibility of missing knock or falsely indicating knock may bereduced.

The inventors herein have developed an engine operating method,comprising: sampling a first knock sensor in a knock window of aselected cylinder via a controller; and sampling a second knock sensorin the knock window of the selected cylinder via the controller inresponse to generating less than a threshold number of knock indicationsbeing generated from sampling of the first knock sensor in the knockwindow of the selected cylinder.

By sampling output of a second knock sensor in response to generatingless than a threshold actual total number of engine knock indicationsbeing generated from sampling output of the first knock sensor, it maybe possible to provide the technical result of improving engine knockdetection during conditions where a knock sensor is degraded. Althoughthe second knock sensor may not provide as desirable a signal to noiseratio as the first sensor with regard to detecting knock in a particularengine cylinder, it may provide a signal that is sufficient fordetecting knock in the particular engine cylinder. The engine knockbackground noise level for the particular cylinder may be reassessedaccording to output of the second knock sensor. Additionally, theapproach provides for adjusting fuel injector and poppet valve openingand closing times to provide additional ways to modify engine backgroundnoise levels so that engine knock detection may be improved.

The present description may provide several advantages. In particular,the approach may improve detection of engine knock. Further, theapproach provides for increasing opportunities to learn engine knockbackground noise levels so that indications of engine knock may be moreaccurate. Further still, the approach may provide ways of changingengine knock background noise levels to improve signal to noise ratiosfor detecting engine knock.

It should be understood that the summary above is provided to introducein simplified form a selection of concepts that are further described inthe detailed description. It is not meant to identify key or essentialfeatures of the claimed subject matter, the scope of which is defineduniquely by the claims that follow the detailed description.Furthermore, the claimed subject matter is not limited toimplementations that solve any disadvantages noted above or in any partof this disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A shows a schematic depiction of an engine system of a vehicle.

FIG. 1B shows example locations for knock sensors for a V8 engine.

FIG. 1C shows an alternative view of knock sensor locations for the V8engine.

FIGS. 2-4 shows a high level flow chart of a way to improve engine knockbackground noise learning opportunities and accuracy of indicatingengine knock; and

FIGS. 5-8 show example engine operating sequences according to themethod of FIGS. 2-4.

DETAILED DESCRIPTION

The following description relates to systems and methods for operatingan engine that includes a knock control system. The engine may be of thetype that is shown in FIGS. 1A-1C. The engine may be operated accordingto the method of FIGS. 2-4. The method may improve opportunities tolearn engine knock background noise levels so that detection of engineknock may be improved. Further, the approach may improve engine knockdetection in the presence of engine knock sensor degradation. The methodof FIGS. 2-4 is at least partially illustrated in the engine operatingsequences of FIGS. 5-8. It should be noted that the present descriptionis not limited to the specific embodiments shown herein and it may beapplied to engines that contain fewer or more engine cylinders.

Turning now to the figures, FIG. 1A depicts an example of a cylinder 14of an internal combustion engine 10, which may be included in a vehicle5. Engine 10 may be controlled at least partially by a control system,including a controller 12, and by input from a human vehicle operator130 via an input device 132. Internal combustion engine 10, comprisingone or more cylinders, one cylinder of which is shown in FIG. 1A, iscontrolled by electronic engine controller 12. The controller 12receives signals from the various sensors shown in FIGS. 1A-1C.Controller 12 employs the actuators shown in FIGS. 1A-1C to adjustengine operation based on the received signals and instructions storedin memory of controller 12. In this example, input device 132 includesan accelerator pedal and a pedal position sensor 134 for generating aproportional pedal position signal. Cylinder (herein, also “combustionchamber”) 14 of engine 10 may include combustion chamber walls 136 witha piston 138 positioned therein. Piston 138 may be coupled to acrankshaft 140 so that reciprocating motion of the piston is translatedinto rotational motion of the crankshaft. Crankshaft 140 may be coupledto at least one vehicle wheel 55 of vehicle 5 via a transmission 54, asfurther described below. Further, a starter motor (not shown) may becoupled to crankshaft 140 via a flywheel to enable a starting operationof engine 10.

In some examples, vehicle 5 may be a hybrid vehicle with multiplesources of torque available to one or more vehicle wheels 55. In otherexamples, vehicle 5 is a conventional vehicle with only an engine or anelectric vehicle with only an electric machine(s). In the example shown,vehicle 5 includes engine 10 and an electric machine 52. Electricmachine 52 may be a motor or a motor/generator. Crankshaft 140 of engine10 and electric machine 52 are connected via transmission 54 to vehiclewheels 55 when one or more clutches 56 are engaged. In the depictedexample, a first clutch 56 is provided between crankshaft 140 andelectric machine 52, and a second clutch 57 is provided between electricmachine 52 and transmission 54. Controller 12 may send a signal to anactuator of each clutch 56 to engage or disengage the clutch, so as toconnect or disconnect crankshaft 140 from electric machine 52 and thecomponents connected thereto, and/or connect or disconnect electricmachine 52 from transmission 54 and the components connected thereto.Transmission 54 may be a gearbox, a planetary gear system, or anothertype of transmission.

The powertrain may be configured in various manners, including as aparallel, a series, or a series-parallel hybrid vehicle. In electricvehicle examples, a system battery 58 may be a traction battery thatdelivers electrical power to electric machine 52 to provide torque tovehicle wheels 55. In some examples, electric machine 52 may also beoperated as a generator to provide electrical power to charge systembattery 58, for example, during a braking operation. It will beappreciated that in other examples, including non-electric vehicleexamples, system battery 58 may be a typical starting, lighting,ignition (SLI) battery coupled to an alternator 46.

Alternator 46 may be configured to charge system battery 58 using enginetorque via crankshaft 140 during engine running. In addition, alternator46 may power one or more electrical systems of the engine, such as oneor more auxiliary systems including a heating, ventilation, and airconditioning (HVAC) system, vehicle lights, an on-board entertainmentsystem, and other auxiliary systems based on their correspondingelectrical demands. In one example, a current drawn on the alternatormay continually vary based on each of an operator cabin cooling demand,a battery charging requirement, other auxiliary vehicle system demands,and motor torque. A voltage regulator may be coupled to alternator 46 inorder to regulate the power output of the alternator based upon systemusage requirements, including auxiliary system demands.

Cylinder 14 of engine 10 can receive intake air via a series of intakepassages 142 and 144 and an intake manifold 146. Intake manifold 146 cancommunicate with other cylinders of engine 10 in addition to cylinder14. One or more of the intake passages may include one or more boostingdevices, such as a turbocharger or a supercharger. For example, FIG. 1Ashows engine 10 configured with a turbocharger, including a compressor174 arranged between intake passages 142 and 144 and an exhaust turbine176 arranged along an exhaust passage 135. Compressor 174 may be atleast partially powered by exhaust turbine 176 via a shaft 180 when theboosting device is configured as a turbocharger. However, in otherexamples, such as when engine 10 is provided with a supercharger,compressor 174 may be powered by mechanical input from a motor or theengine and exhaust turbine 176 may be optionally omitted. In still otherexamples, engine 10 may be provided with an electric supercharger (e.g.,an “eBooster”), and compressor 174 may be driven by an electric motor.In still other examples, engine 10 may not be provided with a boostingdevice, such as when engine 10 is a naturally aspirated engine.

A throttle 162 including a throttle plate 164 may be provided in theengine intake passages for varying a flow rate and/or pressure of intakeair provided to the engine cylinders. For example, throttle 162 may bepositioned downstream of compressor 174, as shown in FIG. 1A, or may bealternatively provided upstream of compressor 174. A position ofthrottle 162 may be communicated to controller 12 via a signal from athrottle position sensor.

An exhaust manifold 148 can receive exhaust gases from other cylindersof engine 10 in addition to cylinder 14. An exhaust gas sensor 126 isshown coupled to exhaust manifold 148 upstream of an emission controldevice 178. Exhaust gas sensor 126 may be selected from among varioussuitable sensors for providing an indication of an exhaust gas air/fuelratio (AFR), such as a linear oxygen sensor or UEGO (universal orwide-range exhaust gas oxygen), a two-state oxygen sensor or EGO, a HEGO(heated EGO), a NOx, a HC, or a CO sensor, for example. In the exampleof FIG. 1A, exhaust gas sensor 126 is a UEGO sensor. Emission controldevice 178 may be a three-way catalyst, a NOx trap, various otheremission control devices, or combinations thereof. In the example ofFIG. 1A, emission control device 178 is a three-way catalyst. Oxygensensor 159 may monitor emission control device 178 for degradation.

Each cylinder of engine 10 may include one or more intake valves and oneor more exhaust valves. For example, cylinder 14 is shown including atleast one intake poppet valve 150 and at least one exhaust poppet valve156 located at an upper region of cylinder 14. In some examples, eachcylinder of engine 10, including cylinder 14, may include at least twointake poppet valves and at least two exhaust poppet valves located atan upper region of the cylinder. In this example, intake valve 150 maybe controlled by controller 12 by cam actuation via cam actuation system152, including one or more cams 151. Similarly, exhaust valve 156 may becontrolled by controller 12 via cam actuation system 154, including oneor more cams 153. The position of intake valve 150 and exhaust valve 156may be determined by valve position sensors (not shown) and/or camshaftposition sensors 155 and 157, respectively.

During some conditions, controller 12 may vary the signals provided tocam actuation systems 152 and 154 to control the opening and closing ofthe respective intake and exhaust valves. The intake and exhaust valvetiming may be controlled concurrently, or any of a possibility ofvariable intake cam timing, variable exhaust cam timing, dualindependent variable cam timing, or fixed cam timing may be used. Eachcam actuation system may include one or more cams and may utilize one ormore of variable displacement engine (VDE), cam profile switching (CPS),variable cam timing (VCT), variable valve timing (VVT), and/or variablevalve lift (VVL) systems that may be operated by controller 12 to varyvalve operation. In alternative examples, intake valve 150 and/orexhaust valve 156 may be controlled by electric valve actuation. Forexample, cylinder 14 may alternatively include an intake valvecontrolled via electric valve actuation and an exhaust valve controlledvia cam actuation, including CPS and/or VCT systems. In other examples,the intake and exhaust valves may be controlled by a common valveactuator (or actuation system) or a variable valve timing actuator (oractuation system).

As further described herein, intake valve 150 and exhaust valve 156 maybe deactivated during VDE mode via electrically actuated rocker armmechanisms. In another example, intake valve 150 and exhaust valve 156may be deactivated via a CPS mechanism in which a cam lobe with no liftis used for deactivated valves. Still other valve deactivationmechanisms may also be used, such as for electrically actuated valves.In one example, deactivation of intake valve 150 may be controlled by afirst VDE actuator (e.g., a first electrically actuated rocker armmechanism, coupled to intake valve 150) while deactivation of exhaustvalve 156 may be controlled by a second VDE actuator (e.g., a secondelectrically actuated rocker arm mechanism, coupled to exhaust valve156). In alternate examples, a single VDE actuator may controldeactivation of both intake and exhaust valves of the cylinder. In stillother examples, a single cylinder valve actuator deactivates a pluralityof cylinders (both intake and exhaust valves), such as all of thecylinders in an engine bank, or a distinct actuator may controldeactivation for all of the intake valves while another distinctactuator controls deactivation for all of the exhaust valves of thedeactivated cylinders. It will be appreciated that if the cylinder is anon-deactivatable cylinder of the VDE engine, then the cylinder may nothave any valve deactivating actuators. Each engine cylinder may includethe valve control mechanisms described herein. Intake and exhaust valvesare held in closed positions over one or more engine cycles whendeactivated so as to prevent flow into or out of cylinder 14.

Cylinder 14 can have a compression ratio, which is a ratio of volumeswhen piston 138 is at bottom dead center (BDC) to top dead center (TDC).In one example, the compression ratio is in the range of 9:1 to 10:1.However, in some examples where different fuels are used, thecompression ratio may be increased. This may happen, for example, whenhigher octane fuels or fuels with a higher latent enthalpy ofvaporization are used. The compression ratio may also be increased ifdirect injection is used due to its effect on engine knock.

Each cylinder of engine 10 may include a spark plug 192 for initiatingcombustion. An ignition system 190 can provide an ignition spark tocombustion chamber 14 via spark plug 192 in response to a spark advancesignal from controller 12, under select operating modes. Spark timingmay be adjusted based on engine operating conditions and driver torquedemand. For example, spark may be provided at minimum spark advance forbest torque (MBT) timing to maximize engine power and efficiency.Controller 12 may input engine operating conditions, including enginespeed, engine load, and exhaust gas AFR, into a look-up table and outputthe corresponding MBT timing for the input engine operating conditions.In other examples, spark may be retarded from MBT, such as to expeditecatalyst warm-up during engine start or to reduce an occurrence ofengine knock.

In some examples, each cylinder of engine 10 may be configured with oneor more fuel injectors for providing fuel thereto. As a non-limitingexample, cylinder 14 is shown including a direct fuel injector 166 and aport fuel injector 66. Fuel injectors 166 and 66 may be configured todeliver fuel received from a fuel system 8. Fuel system 8 may includeone or more fuel tanks, fuel pumps, and fuel rails. Fuel injector 166 isshown coupled directly to cylinder 14 for injecting fuel directlytherein in proportion to a pulse width of a signal received fromcontroller 12. Port fuel injector 66 may be controlled by controller 12in a similar way. In this manner, fuel injector 166 provides what isknown as direct injection (hereafter also referred to as “DI”) of fuelinto cylinder 14. While FIG. 1A shows fuel injector 166 positioned toone side of cylinder 14, fuel injector 166 may alternatively be locatedoverhead of the piston, such as near the position of spark plug 192.Such a position may increase mixing and combustion when operating theengine with an alcohol-based fuel due to the lower volatility of somealcohol-based fuels. Alternatively, the injector may be located overheadand near the intake valve to increase mixing. Fuel may be delivered tofuel injectors 166 and 66 from a fuel tank of fuel system 8 via fuelpumps and fuel rails. Further, the fuel tank may have a pressuretransducer providing a signal to controller 12.

Fuel injectors 166 and 66 may be configured to receive different fuelsfrom fuel system 8 in varying relative amounts as a fuel mixture andfurther configured to inject this fuel mixture directly into cylinder.For example, fuel injector 166 may receive alcohol fuel and fuelinjector 66 may receive gasoline. Further, fuel may be delivered tocylinder 14 during different strokes of a single cycle of the cylinder.For example, directly injected fuel may be delivered at least partiallyduring a previous exhaust stroke, during an intake stroke, and/or duringa compression stroke. Port injected fuel may be injected after intakevalve closing of a previous cycle of the cylinder receiving fuel and upuntil intake valve closing of the present cylinder cycle. As such, for asingle combustion event (e.g., combustion of fuel in the cylinder viaspark ignition), one or multiple injections of fuel may be performed percycle via either or both injectors. The multiple DI injections may beperformed during the compression stroke, intake stroke, or anyappropriate combination thereof in what is referred to as split fuelinjection.

Fuel tanks in fuel system 8 may hold fuels of different fuel types, suchas fuels with different fuel qualities and different fuel compositions.The differences may include different alcohol content, different watercontent, different octane, different heats of vaporization, differentfuel blends, and/or combinations thereof, etc. One example of fuels withdifferent heats of vaporization includes gasoline as a first fuel typewith a lower heat of vaporization and ethanol as a second fuel type witha greater heat of vaporization. In another example, the engine may usegasoline as a first fuel type and an alcohol-containing fuel blend, suchas E85 (which is approximately 85% ethanol and 15% gasoline) or M85(which is approximately 85% methanol and 15% gasoline), as a second fueltype. Other feasible substances include water, methanol, a mixture ofalcohol and water, a mixture of water and methanol, a mixture ofalcohols, etc. In still another example, both fuels may be alcoholblends with varying alcohol compositions, wherein the first fuel typemay be a gasoline alcohol blend with a lower concentration of alcohol,such as E10 (which is approximately 10% ethanol), while the second fueltype may be a gasoline alcohol blend with a greater concentration ofalcohol, such as E85 (which is approximately 85% ethanol). Additionally,the first and second fuels may also differ in other fuel qualities, suchas a difference in temperature, viscosity, octane number, etc. Moreover,fuel characteristics of one or both fuel tanks may vary frequently, forexample, due to day to day variations in tank refilling.

Controller 12 is shown in FIG. 1A as a microcomputer, including amicroprocessor unit 106, input/output ports 108, an electronic storagemedium for executable programs (e.g., executable instructions) andcalibration values shown as non-transitory read-only memory chip 110 inthis particular example, random access memory 112, keep alive memory114, and a data bus. Controller 12 may receive various signals fromsensors coupled to engine 10, including signals previously discussed andadditionally including a measurement of inducted mass air flow (MAF)from a mass air flow sensor 122; an engine coolant temperature (ECT)from a temperature sensor 116 coupled to a cooling sleeve 118; anexhaust gas temperature from a temperature sensor 158 coupled to exhaustpassage 135; a crankshaft position signal from a Hall effect sensor 120(or other type) coupled to crankshaft 140; throttle position from athrottle position sensor 163; signal UEGO from exhaust gas sensor 126,which may be used by controller 12 to determine the air-fuel ratio ofthe exhaust gas; oxygen sensor 159; engine vibrations (e.g., caused byknock) via vibration sensing knock sensor 90; and an absolute manifoldpressure signal (MAP) from a MAP sensor 124. An engine speed signal,RPM, may be generated by controller 12 from crankshaft position. Themanifold pressure signal MAP from MAP sensor 124 may be used to providean indication of vacuum or pressure in the intake manifold. Controller12 may infer an engine temperature based on the engine coolanttemperature and infer a temperature of emission control device 178 basedon the signal received from temperature sensor 158.

Controller 12 receives signals from the various sensors of FIG. 1A andemploys the various actuators of FIG. 1A to adjust engine operationbased on the received signals and instructions stored on a memory of thecontroller. For example, the controller may transition the engine tooperating in VDE mode by actuating valve actuators 152 and 154 todeactivate selected cylinders, as further described with respect to FIG.5.

As described above, FIG. 1A shows only one cylinder of a multi-cylinderengine. As such, each cylinder may similarly include its own set ofintake/exhaust valves, fuel injector(s), spark plug, etc. It will beappreciated that engine 10 may include any suitable number of cylinders,including 2, 3, 4, 5, 6, 8, 10, 12, or more cylinders. Further, each ofthese cylinders can include some or all of the various componentsdescribed and depicted by FIG. 1A with reference to cylinder 14.

During selected conditions, such as when the full torque capability ofengine 10 is not requested, one of a first or a second cylinder groupmay be selected for deactivation by controller 12 (herein also referredto as a VDE mode of operation). During the VDE mode, cylinders of theselected group of cylinders may be deactivated by shutting offrespective fuel injectors 166 and 66. Further, valves 150 and 156 may bedeactivated and held closed over one or more engine cycles. While fuelinjectors of the disabled cylinders are turned off, the remainingenabled cylinders continue to carry out combustion, with correspondingfuel injectors and intake and exhaust valves active and operating. Tomeet torque requirements, the controller adjusts the amount of airentering active engine cylinders. Thus, to provide equivalent enginetorque that an eight cylinder engine produces at 0.2 engine load and aparticular engine speed, the active engine cylinders may operate athigher pressures than engine cylinders when the engine is operated withall engine cylinders being active. This requires higher manifoldpressures, resulting in lowered pumping losses and increased engineefficiency. Additionally, the lower effective surface area (from onlythe active cylinders) exposed to combustion reduces engine heat losses,increasing the thermal efficiency of the engine.

Referring now to FIG. 1B, a plan view of engine 10 is shown. Front 10 aof engine 10 may include a front end accessory drive (FEAD) (not shown)to provide power to an alternator, power steering system, and airconditioning compressor. In this example, engine 10 is shown in a V8configuration with eight cylinders that are numbered 1-8. Engine knockmay be sensed via four knock sensors 90 a-90 d. The knock sensors arepositioned in the valley of engine block 9. In this example, output ofknock sensor 90 a is sampled via controller 12 during the knock windows(e.g., crankshaft angular intervals) of engine cylinders one and two.Thus, knock sensor 90 a is associated with cylinders one and two.However, if knock sensor 90 a (the primary knock sensor of cylindernumbers one and two) is suspected of being degraded, output of knocksensor 90 b (the secondary knock sensor of cylinder numbers one and two)may be sampled or measured in knock windows associated with enginecylinder numbers one and two. Output of knock sensor 90 b is sampled viacontroller 12 during the knock windows of engine cylinders three andfour. However, if knock sensor 90 b (the primary knock sensor ofcylinder numbers three and four) is suspected of being degraded, outputof knock sensor 90 a (the secondary knock sensor of cylinder numbersthree and four) may be sampled or measured in knock windows associatedwith engine cylinder numbers three and four. Thus, knock sensor 90 b isassociated with cylinders three and four. Output of knock sensor 90 c issampled via controller 12 during the knock windows of engine cylindersfive and six. Thus, knock sensor 90 c is associated with cylinders fiveand six. However, if knock sensor 90 c (the primary knock sensor ofcylinder numbers five and six) is suspected of being degraded, output ofknock sensor 90 d (the secondary knock sensor of cylinder numbers fiveand six) may be sampled or measured in knock windows associated withengine cylinder numbers five and six. Output of knock sensor 90 d issampled via controller 12 during the knock windows of engine cylinders 7and 8. Thus, knock sensor 90 d is associated with cylinders seven andeight. However, if knock sensor 90 d (the primary knock sensor ofcylinder numbers seven and eight) is suspected of being degraded, outputof knock sensor 90 c (the secondary knock sensor of cylinder numbersseven and eight) may be sampled or measured in knock windows associatedwith engine cylinder numbers seven and eight. The plurality of knocksensors improves the ability to detect knock for each cylinder sinceattenuation of engine vibrations from knock increases as the distancefrom the knocking cylinder to the knock sensor increases. Knock sensoroutput is not sampled when the knock windows are closed.

Referring now to FIG. 1C, a front view of engine 10 is shown. Engineblock 9 includes a valley 10 b where engine knock sensors 90 a and 90 care mounted to block 9. By mounting knock sensors 90 a and 90 c in thevalley 10 b, a good signal to noise ratio may be available so that knockmay be more reliably detected. However, the mounting locations of knocksensors 90 a-90 d may also allow some fuel injector control actions tobe observed by some sensors and not by others. Thus, background noiselevels of some cylinders may be higher or lower than other cylinders.Additionally, the distance of a fuel injector that opens or closes neara knock window of another engine cylinder may affect an amount of timethat it takes for a vibration to travel from the operating fuel injectorto the knock sensor. And, a longer time for the vibration to travel fromthe fuel injector to the knock sensor may allow the vibration to enter aknock window for a cylinder. As such, knock sensor location, firingorder, and engine configuration may also affect engine knock backgroundnoise levels for some engine cylinders.

Thus, the system of FIGS. 1A-1C provides for a system for operating anengine, comprising: an engine including at least one vibration sensingengine knock sensor; and a controller including executable instructionsstored in non-transitory memory to adjust poppet valve timing of theengine via the controller in response to a request to learn one or moreengine knock background noise levels. The system further comprisesadditional instructions to adjust fuel injector timing in response tothe request to the request to learn one or more engine knock backgroundnoise levels. The system includes where the request to learn one or moreengine knock background noise levels is based on a distance traveled bya vehicle. The system includes where the request to learn one or moreengine knock background noise levels is based on an amount of time theengine has operated since manufacturing of the engine. The systemfurther comprises additional instructions to adjust a cylinder firingpattern in response to the request to learn one or more engine knockbackground noise levels. The system further comprises additionalinstructions to adjust a cylinder firing density in response to therequest to learn one or more engine knock background noise levels.

Referring now to FIGS. 2-4, a method for operating an engine is shown.The method of FIGS. 2-4 may be included in and may cooperate with thesystem of FIGS. 1A-1C. At least portions of method 200 may beincorporated in the system of FIGS. 1A-1C as executable instructionsstored in non-transitory memory. In addition, other portions of method200 may be performed via a controller transforming operating states ofdevices and actuators in the physical world. The controller may employengine actuators of the engine system to adjust engine operation.Further, method 200 may determine selected control parameters fromsensor inputs. The engine may be rotating and combusting fuel when themethod of FIGS. 2-4 is performed.

At 202, method 200 determines vehicle and engine operating conditionsvia the sensors described in FIG. 1A-1C. Method 200 may determineoperating conditions including but not limited to engine speed, engineload, engine temperature, ambient temperature, fuel injection timing,knock sensor output, fuel type, fuel octane, engine position, engine airflow, change in cylinder air flow, and change in engine speed. Method200 proceeds to 204.

At 204, method 200 judges if an engine knocking rate (e.g., an actualtotal number of knock indications for a selected engine cylinder in aspecified time or distance traveled interval (10 indications of knock incylinder number one in five minutes)) of a selected cylinder (e.g.,cylinder j, where j is the cylinder number) or an actual total number ofknock indications for the selected cylinder is greater than a firstthreshold value for present engine speed and engine load. Method 200 mayrecord indications of knock in each cylinder and determine an amount oftime it took for the indications of knock to occur for the selectedcylinder. If method 200 judges that the engine knocking rate of aselected cylinder or an actual total number of knock indications for theselected cylinder is greater than a first threshold value for presentengine speed and engine load, then the answer is yes and method 200proceeds to 220. Otherwise, the answer is no and method 200 proceeds to206. A request to diagnose or adjust the engine knock background noiselevels for the selected cylinder may be generated when method 200 judgesthat an engine knocking rate of the selected cylinder or an actual totalnumber of knock indications for the selected cylinder is greater than afirst threshold value for present engine speed and engine load.

At 206, method 200 judges if an engine knocking rate of a selectedcylinder or an actual total number of knock indications for the selectedcylinder is less than a second threshold value for present engine speedand engine load. If method 200 judges that the engine knocking rate of aselected cylinder or an actual total number of knock indications for theselected cylinder is less than a second threshold value for presentengine speed and engine load, then the answer is yes and method 200proceeds to 240. Otherwise, the answer is no and method 200 proceeds to208. A request to diagnose or adjust the engine knock background noiselevels for the selected cylinder may be generated when method 200 judgesthat an engine knocking rate of the selected cylinder or an actual totalnumber of knock indications for the selected cylinder is less than asecond threshold value for present engine speed and engine load.

At 208, method 200 judges if an engine operating time (e.g., a totalamount of time the engine has been combusting fuel since the engine wasmanufactured) exceeds a third threshold value or if a distance traveledby a vehicle (e.g., a total distance that the vehicle as traveled sincethe vehicle was manufactured) that includes the engine exceeds a forththreshold value. If method 200 judges that an engine operating timeexceeds the third threshold value or if a distance traveled by a vehiclethat includes the engine exceeds a forth threshold value, then theanswer is yes and method 200 proceeds to 209. Otherwise, the answer isno and method 200 proceeds to 210. A request to adjust the engine knockbackground noise levels for the selected cylinder may be generated whenmethod 200 judges that an engine operating time exceeds a thirdthreshold value or if a distance traveled by a vehicle that includes theengine exceeds a forth threshold value.

At 210, method 200 judges if all engine knock background noise levelsfor the present engine speed and load have been determined. The engineknock background noise levels may include but are not limited to thefollowing engine knock background noise levels for conditions when allengine cylinders are operating: the total engine knock background noiselevel (Cyl_bkg_noise(j)), engine knock base noise level(Cyl_base_noise(j)) that does not include noise from poppet valves orfuel injectors closing during a knock window of cylinder (j), engineknock injector closing noise level (Cyl_inj_cnoise(j)) that does notinclude base engine noise or poppet valve noise during the knock windowof cylinder (j), engine knock injector opening noise level(Cyl_inj_onoise_(j)) that does not include base engine noise or poppetvalve noise during the knock window of cylinder (j), engine intakepoppet valve noise level (Cyl_ivlv_noise(j)) that does not include baseengine noise or fuel injector opening or closing noise generated duringthe knock window of cylinder (j), engine exhaust poppet valve noiselevel (Cyl_evlv_noise(j)) that does not include base engine noise orfuel injector opening or closing noise generated during the knock windowof cylinder (j), and where j is the cylinder number of the engine.

In addition, method 200 may judge if engine knock background noiselevels (e.g., Cyl_bkg_noise(j), Cyl_base_noise(j), Cyl_inj_cnoise(j),Cyl_inj_onoise (j), Cyl_ivlv_noise(j), and Cyl_evlv_noise(j))specifically applied to each engine operating mode that is available atthe present engine speed and load including but not limited to cylinderfiring patterns (e.g., firing an eight cylinder engine in a fourcylinder mode with a firing order of 1-7-6-4-1-7-6-4), cylinder firingfraction or density (e.g., cylinder firing fraction is an actual totalnumber of cylinder firing events (e.g., combustion in a cylinder duringa cycle of the cylinder) divided by an actual total number of cylindercompression strokes over a predetermined actual total number of cylindercompression strokes), split fuel injection (e.g., where one or more fuelinjectors inject fuel twice or more to a cylinder during a cycle of thecylinder), direct injection only mode (e.g., where fuel is injected to acylinder only via a direct injector and not via a port injector during acycle of the cylinder), port injection only mode (e.g., where fuel isinjected to a cylinder only via a port injector and not via a directinjector during a cycle of the cylinder), and port and direct fuelinjection mode (e.g., where fuel is injected to a cylinder via a directinjector and a port injector during a cycle of the cylinder) have beendetermined. Note that unique engine knock background noise levels may beprovided for each cylinder firing pattern, cylinder firing density,split fuel injection, direct injection only mode, port injection onlymode, and port and direct fuel injection mode since engine knockbackground noise levels may be influenced by unique fuel injector noiseand unique poppet valve noise in each of these engine operating modes.

Engine knock background noise levels for the present engine speed andload may be stored in tables and/or functions. A byte of data thatindicates whether or not the particular table or function entry has beenlearned in the past for the present engine speed and engine load may beincluded in memory for each table entry or function entry. If method 200judges that all the engine knock background noise levels for the presentengine speed and engine load have been adjusted, then the answer is yesand method 200 proceeds to 211. Otherwise, the answer is no and method200 proceeds to 212.

At 211, method 200 assesses whether or not knock should be indicated forthe selected cylinder that is being evaluated for engine knock (e.g.,cylinder j). In one example, method 200 computes a knock intensity valuefor cylinder j by integrating sampled output of the knock sensor duringthe knock window of cylinder j and dividing the integrated knock sensoroutput by the total engine knock background noise level of cylinder jfor the present engine speed and engine load. If the knock intensityvalue exceeds a threshold value (e.g., 2), then knock is indicated forthe cylinder j and spark timing for the cylinder j is retarded by apredetermined amount. The spark is retarded for cylinder j and then thespark timing is advanced back toward the MBT (minimum spark advance forbest engine torque at the present engine speed and load) spark timingfor cylinder j. For example, if the knock intensity value for cylindernumber one exceeds a threshold level, then knock is indicated forcylinder number one and spark timing of cylinder number one is retardedby five crankshaft degrees. The spark timing for cylinder number one maybe advanced by five crankshaft degrees within ten seconds of when thespark timing of cylinder number one was retarded based on knock. Ifknock is not indicated, spark timing for the cylinder remains at itsrequested or base timing (e.g., knock limited spark timing or MBTtiming). The presence or absence of engine knock for each cylinder maybe determined in this way. The cylinder number j may be adjustedaccording to an engine firing order each engine cycle (e.g., tworevolutions) so that knock is evaluated for each engine cylinder eachengine cycle. Method 200 proceeds to exit after adjusting engine sparktiming in cylinder j for engine knock.

At 212, method 200 determines engine knock background noise levels forthe present engine speed and load for which values have not beendetermined. As described at 210, engine knock background noise levelsfor the present engine speed and load may be stored in tables and/orfunctions. A byte of data that indicates whether or not the particulartable or function entry has been learned in the past for the presentengine speed and engine load may be included in memory for each tableentry or function entry. If one or more engine knock background noiselevels, including engine knock background noise levels for particularcylinder firing patterns, cylinder firing densities, fuel injectionmodes, and poppet valve modes has not been determined or has beensubject to a request to relearn the value stored therein, then theengine knock background noise level entries in the table or function areidentified and marked for being learned. The entries of the tables orfunction may be individually numbered and method 200 may begin learningengine knock background noise levels of low numbered entries. Method 200may learn engine knock background noise level entries in the tables orfunctions in ascending order from low numbered entries to high numberedentries. Method 200 may increment the entry number until all engineknock background noise level entries that are desired to be learned havebeen learned. Engine knock background noise levels may be learned foreach engine cylinder. Method 200 proceeds to 214 after identifyingengine knock background noise levels that are to be learned.

At 214, method 200 adjusts engine operating modes so that engine knockbackground noise levels that may be associated with the engine operatingmodes may be learned. The engine knock background noise levels may belearned for engine operating modes that are available for the presentengine speed and engine load. Available engine operating modes includeengine operating modes that may provide the requested driver demandtorque or engine load at the present engine speed. Thus, if the engineis a four stroke V8 engine that may operate with two active (e.g.,combustion in the cylinders) cylinders and six deactivated cylinders tomeet the present driver demand torque at the present engine speed, thenone or more two cylinder operating modes may be available to be engagedto operate the engine. Further, if learning of engine knock backgroundnoise levels is requested for a four stroke V8 engine having an allcylinder operating firing order of 1-3-7-2-6-5-4-8, the engine beingavailable to operate in a variable displacement mode where the engineoperates with four cylinders combusting fuel and four cylindersdeactivated with a firing order of 1-7-6-4, then four of the engine'scylinders may be deactivated so that the engine operates with fouractive cylinders and a firing order of 1-7-6-4. The engine knockbackground noise levels may be learned for four or all eight cylinderswhen the engine is operated with four active cylinders. In particular,engine knock background noise levels may be learned for the fourcombusting cylinders and for the four cylinders that are not combusting.

The knock windows of the deactivated cylinders are free and unutilizedto detect knock in the deactivated cylinders (as no combustion is takingplace), and therefore can be reused to measure engine knock backgroundnoise that may or may not include injector and/or valve noises from theactivated cylinders. The knock windows of the activated cylinders areutilized to detect knock (in the activated cylinders). But the knockwindow of an activated cylinder can be freed if needed by retarding itsspark timing so non-knocking conditions are ensured, and reused tomeasure engine knock background noise that may or may not includeinjector and/or valve noises from the other activated cylinders.

The engine's operating mode may be changed to learn engine knockbackground noise levels that have not been previously learned so thatopportunities to learn engine knock background noise levels may beincreased. Changing the engine's operating mode may include but is notlimited to changing the engine's fuel injection mode (e.g., portinjection (PI) only, direct injection (DI) only, DI and PI, splitinjection), changing intake and exhaust poppet valve timing, andchanging the engine cylinder firing density or cylinder firing pattern.By changing the engine's operating mode, engine knock background noiselevels that may otherwise not be learned, may be learned. For example,for a V8 engine with firing order 1-3-7-2-6-5-4-8, the direct injectionof cylinder i may fall into the knock window of cylinder j wherecylinder j fires 3 events (270 crank angle degrees) after cylinder i(e.g., i=1 and j=2). To learn the injector noise of cylinder j (e.g., 2)interfering with the knock window of cylinder i (e.g., 1) cylinder j(e.g., 2) may be activated and cylinder i (e.g., 1) may be deactivated(to avoid knocking of cylinder i to affect the knock background noise).This case is not encountered when the V8 engine operates at a firingdensity of ⅔. Changing the firing density to ¾ (while maintaining sametorque demand) will allow learning of injector noise of cylinder j.Method 200 proceeds to 216.

At 216, method 200 determines engine knock background noise levels viafiltering and integrating engine knock sensor output that occurs duringthe engine knock window of the selected cylinder. For example, output ofa particular knock sensor may be sampled or measured and integratedwhile a knock window of a particular cylinder is open. The integratedvalue may be an engine knock base noise level or another engine knocknoise level. Further, the present engine knock background noise levelmay be constructed from an average of a predetermined number of pastengine knock background noise levels for the selected cylinder. Theengine may enter a new operating mode for each engine knock backgroundnoise level in the table or function that is requested to be learned,and each engine knock background noise level in the table or functionmay be learned from sampling and integrating output of a knock sensorduring at least a portion of a cylinder knock window. Method 200 returnsto 210 after determining the background noise level for each engineknock background noise entry that has been requested to be learned.

At 209, method 200 requests that all engine knock background noiselevels be relearned. Thus, each entry of the tables or functions thatcontain engine knock background noise levels may be marked as an entrythat is to be learned. Once an entry in a table or function is learned,it may be marked as learned so that it is not relearned unless it isrequested to be learned again. Method 200 proceeds to 212.

At 220, method 200 retards spark timing of a selected cylinder. Theselected cylinder may be a cylinder for which it is desired to determineengine knock background noise levels (e.g., Cyl_bkg_noise(j),Cyl_base_noise(j), Cyl_inj_cnoise(j), Cyl_inj_onoise (j),Cyl_ivlv_noise(j), and Cyl_evlv_noise(j)). The spark timing of theselected cylinder is retarded so that knock does not occur in theselected cylinder so that the engine knock background noise levels maybe reliable. Method 200 proceeds to 222.

At 222, method 200 determines engine knock background noise levels forthe present engine operating conditions (e.g., engine speed, engineload, and engine operating mode) via filtering and integrating engineknock sensor output that occurs during the engine knock window of theselected cylinder. The integrated value may be an engine knock basenoise level or another engine knock noise level. Further, the presentengine knock background noise levels may be constructed from an averageof a predetermined number of past engine knock background noise levelsfor the selected cylinder. Method 200 proceeds to 224 after engine knockbackground noise levels for the selected cylinder have been learned.

At 224, method 200 judges if one or more of the engine knock backgroundnoise levels determined at 222 is greater than one or more of the engineknock background noise levels presently associated with the presentengine operating conditions. For example, if the previously determinedvalue of Cyl_base_noise for the selected cylinder at the present engineoperating conditions is 0.5 and the value of Cyl_base_noise determinedat 222 for the selected cylinder at the present engine operatingconditions is 0.75, then the answer is yes and method 200 proceeds to226. If method 200 judges that one or more of the engine knockbackground noise levels determined at 222 is greater than one or more ofthe engine knock background noise levels presently associated with thepresent engine operating conditions, then the answer is yes and method200 proceeds to 226. Otherwise, the answer is no and method 200 proceedsto 230.

A yes answer may be indicative of one or more engine knock backgroundnoise levels being lower than is desired. This may allow the controlsystem to generate more engine knocking indications than may beexpected. Note that a greater number of knock events may be indicated ifthe engine background noise level is lower than is expected becauseintegrated knock sensor output is divided by the engine knock backgroundnoise level. A no answer may be indicative of fuel injector degradationor intake/exhaust poppet valve operation degradation.

At 226, method 200 replaces the values of engine knock background noiselevels for present engine operating conditions with values determined at222. The new engine knock background noise levels may reduce the actualtotal number of engine knock indications since the engine knockbackground noise levels are increased. Method 200 proceeds to 228.

At 228, method 200 assesses whether or not engine knock should beindicated for the selected cylinder based on the newly determined engineknock background noise levels (e.g., the total engine knock backgroundnoise level for the selected cylinder, which includes base, injector,and poppet valve noise levels). In one example, method 200 computes aknock intensity value for the cylinder by integrating sampled output ofthe knock sensor during the knock window of cylinder and dividing theintegrated knock sensor output by the total engine knock backgroundnoise level for the selected cylinder. If the knock intensity valueexceeds a threshold value (e.g., 2), then knock is indicated for theselected cylinder and spark timing for the selected cylinder may beretarded by a predetermined amount. The spark is retarded for theselected cylinder and then the spark timing is advanced back toward theMBT (minimum spark advance for best engine torque at the present enginespeed and load) spark timing for the selected cylinder. For example, ifthe knock intensity value for cylinder number one exceeds a thresholdlevel, then knock is indicated for cylinder number one and spark timingof cylinder number one is retarded by five crankshaft degrees. The sparktiming for cylinder number one may be advanced by five crankshaftdegrees within ten seconds of when the spark timing of cylinder numberone was retarded based on knock. If knock is not indicated, spark timingfor the selected cylinder remains at its requested or base timing (e.g.,knock limited spark timing or MBT timing). Knock for each cylinder maybe determined in this way. Method 200 proceeds to exit after indicatingor not indicating knock for the selected cylinder.

At 230, method 200 judges if one or more of the engine knock backgroundnoise levels determined at 222 decreased by more than a thresholdamount. For example, if the previously determined value ofCyl_base_noise for the selected cylinder at the present engine operatingconditions is 0.5 and the value of Cyl_base_noise determined at 222 forthe selected cylinder at the present engine operating conditions is0.25, then it may be determined that the engine knock background noiselevel has decreased by more than a threshold amount (e.g., 0.1). Ifmethod 200 judges that one or more of the engine knock background noiselevels determined at 222 has decreased from one or more of the engineknock background noise levels presently associated with the presentengine operating conditions by more than a threshold amount, then theanswer is yes and method 200 proceeds to 232. Otherwise, the answer isno and method 200 proceeds to 231. A yes answer may be indicative offuel injector or poppet valve degradation.

At 232, method 200 request diagnostics for fuel injectors and/or poppetvalves. For example, method 200 may request an increase or decrease inthe amount of fuel injected via a fuel injector to determine if the fuelinjector is operating as desired. Further, method 200 may requestadvancing or retarding of intake and/or exhaust valves to determine ifvalve timing is moving as commanded. Method 200 proceeds to exit.

At 231, method 200 may adjust spark timing to compensate for fuelproperties (e.g., low fuel octane). By retarding the spark timing forengine cylinders, engine knock that may be related to fuels withespecially low octane levels may be reduced. Method 200 proceeds toexit.

At 240, method 200 retards spark timing of a selected cylinder. Theselected cylinder may be a cylinder for which it is desired to determineengine knock background noise levels (e.g., Cyl_bkg_noise(j),Cyl_base_noise(j), Cyl_inj_cnoise(j), Cyl_inj_onoise (j),Cyl_ivlv_noise(j), and Cyl_evlv_noise(j)). The spark timing of theselected cylinder is retarded so that knock does not occur in theselected cylinder so that the engine knock background noise levels maybe reliable. Method 200 proceeds to 242.

At 242, method 200 adjusts DI open/closing timing, PI open/closingtiming, intake valve opening/closing timing, and/or exhaust valveopening/closing timing so that the engine knock background noise levelmay be lowered to improve the signal to noise ratio of knock sensoroutput to improve knock detection. The PI timing, DI timing, intakepoppet valve timing, and exhaust poppet valve timing may be advanced orretarded to decrease noise in the engine knock window of the selectedcylinder. An example of fuel injector timing adjustments is shown inFIG. 7. An example of poppet valve timing adjustments is shown in FIG.8. Of course, the fuel injection timing and poppet valve timingadjustments may also be made to increase engine knock background noiselevels in engine knock windows, if desired. Further, the fuel injectiontiming and poppet valve timing adjustments may be made to decreaseengine noise levels in engine knock windows for other reasons (e.g., toverify engine knock background levels for other engine cylinders, etc.),if desired. Method 200 proceeds to 244 after adjusting injector andpoppet valve opening and closing timings relative to crankshaftposition.

At 244, method 200 determines engine knock background noise levels forthe present engine operating conditions (e.g., engine speed, engineload, and engine operating mode) via filtering and integrating engineknock sensor output that occurs during the engine knock window of theselected cylinder. The integrated value may be an engine knock basenoise level or another engine knock noise level. Further, the presentengine knock background noise levels may be constructed from an averageof a predetermined number of past engine knock background noise levelsfor the selected cylinder. Method 200 proceeds to 246 after engine knockbackground noise levels for the selected cylinder have been learned.

At 246, method 200 judges if an engine knocking rate of a selectedcylinder or an actual total number of knock indications for the selectedcylinder is less than the second threshold value for present enginespeed and engine load. If method 200 judges that the engine knockingrate of the selected cylinder or an actual total number of knockindications for the selected cylinder is less than the second thresholdvalue for present engine speed and engine load, then the answer is yesand method 200 proceeds to 248. Otherwise, the answer is no and method200 proceeds to 208.

At 248, method 200 changes the knock sensor of the selected cylinderthat is sampled or measured. The knock sensor is changed so that engineknock may be determined in the selected cylinder via a secondary knocksensor instead of a primary knock sensor that is associated with thecylinder. For example, if indications of knock in cylinder number oneare less than the second threshold and cylinder number one is theselected cylinder, then knock sensor 90 b may be sampled to determineknock in cylinder number one instead of knock sensor 90 a. This mayallow knock to be detected in cylinder number one even if the primaryknock sensor of cylinder number one is degraded. Method 200 also learnsengine knock background noise levels via sampling the output of thesecondary knock sensor of the selected cylinder. Method 200 proceeds to250.

At 250, method 250 assesses whether or not knock should be indicated forthe selected cylinder based on output of the secondary knock sensor thatis sampled during the knock window of the selected cylinder. Method 200computes a knock intensity value for the selected cylinder byintegrating sampled output of the knock sensor during the knock windowof selected cylinder and dividing the integrated knock sensor output bythe total engine knock background noise level for the selected cylinderas determined from output of the secondary knock sensor. If the knockintensity value exceeds a threshold value (e.g., 2), then knock isindicated for the selected cylinder and spark timing for the selectedcylinder may be retarded by a predetermined amount. The spark isretarded for the selected cylinder and then the spark timing is advancedback toward the MBT (minimum spark advance for best engine torque at thepresent engine speed and load) spark timing for the selected cylinder.If knock is not indicated, spark timing for the selected cylinderremains at its requested or base timing (e.g., knock limited sparktiming or MBT timing). Knock for each cylinder may be determined in thisway. Method 200 proceeds to 208.

In these ways, the opportunities to learn engine knock background noiselevels of each cylinder may be increased. Further, the selected cylindermentioned in the description of method 200 may be incremented,decremented, or otherwise adjusted so that each cylinder of the enginemay be the selected cylinder once during an engine cycle (e.g., twocrankshaft revolutions). Further still, a knock sensor that isassociated with a knock window of a cylinder may be changed to improvethe possibility of knock detection during conditions of knock sensordegradation or other conditions when it may be desirable to do so (e.g.,when comparing engine knock background noise levels of the variouscylinders, performing engine diagnostics, etc.).

Referring now to FIG. 5, a timing sequence 500 that illustrates examplebase engine knock window timing, direct injector timing, and intake andexhaust poppet valve opening and closing timing is shown. Theillustrated timings are for an eight cylinder engine that has a firingorder of 1-3-7-2-6-5-4-8. The engine is a four stroke engine that has acycle of 720 crankshaft degrees. The engine crankshaft degrees arelocated along the horizontal axis and zero degrees representstop-dead-center compression stroke for cylinder number one. The eightcylinders are labeled along the vertical axis. In this example, severalengine knock background noise influences are shown visually by DIinjections and poppet valve timings.

The engine knock windows for each cylinder are positioned at a level ofa tick mark along the vertical axis that is associated with the knockwindow. For example, the engine knock window for or associated withcylinder number one is indicated by slash bar 501. Knock windows for theremaining engine cylinders (2-8) are indicated by bars (502-508) thatalign with labeling along the vertical axis. The controller may sample(e.g., measure) output of the knock sensor when a knock window of acylinder is open. An open knock window is a crankshaft region whereengine knock may be expected for a particular engine cylinder.

Knock window 501 includes a slash pattern that indicates that output ofknock sensor 90 a is sampled during the open knock window of cylindernumber one. Knock window 504 includes the same slash pattern thatindicates that output of knock sensor 90 a is sampled during the openknock window of cylinder number two. Knock window 502 includes a plaidpattern that indicates that output of knock sensor 90 b is sampledduring the open knock window of cylinder number three. Knock window 507also includes a plaid pattern that indicates that output of knock sensor90 b is sampled during the open knock window of cylinder number four.Knock window 506 includes a horizontal line pattern that indicates thatoutput of knock sensor 90 c is sampled during the open knock window ofcylinder number five. Knock window 505 includes the same horizontal linepattern that indicates that output of knock sensor 90 c is sampledduring the open knock window of cylinder number six. Knock window 503includes a vertical line pattern that indicates that output of knocksensor 90 c is sampled during the open knock window of cylinder numberseven. Knock window 508 also includes a vertical line pattern thatindicates that output of knock sensor 90 c is sampled during the openknock window of cylinder number eight. Thus, the knock sensor that issampled during a particular knock window is indicated by the patterncontained within the knock window.

The engine fuel injection timings for each cylinder are positioned at alevel the tick mark along the vertical axis that is associated with thefuel injection. For example, solid bar 510 represents a DI fuel injectoropen interval for cylinder number two. The DI fuel injector for cylindernumber two is closed when solid bar 510 is not visible. The DI fuelinjector for cylinder number two opens at the left side of solid bar 510and closes at the right side of solid bar 510. DI fuel injections forthe remaining engine cylinders (2-8) are indicated by similar solid bars(511-517) and they follow the same convention as solid bar 510. The fuelinjector bars 510-517 respectively align with cylinders listed along thevertical axis that the fuel injector bars correspond to.

The strokes of a cylinder are positioned just above a level the tickmark along the vertical axis that is associated with the stroke. Forexample, strokes for cylinder number one are indicated by horizontallines 520-523. Letters p, e, i, and c identify the power (p), exhaust(e), intake (i), and compression (c) strokes associated with cylindernumber one. Strokes for the other engine cylinders are identified in asimilar way by lines 525-558.

The exhaust valve timings for each cylinder are positioned above a levelthe tick mark along the vertical axis that is associated with theexhaust valve timings. For example, exhaust valve opening time forcylinder number one is indicated by cross-hatched bar 560. The exhaustvalves for cylinder number one are closed when no cross-hatched bar ispresent above the cylinder strokes of cylinder number one. Exhaust valveopening times for the other cylinders are indicated at 562, 564, 567,570, 572, 574, 575, 577, and 578.

The intake valve timings for each cylinder are positioned above a levelthe tick mark along the vertical axis that is associated with the intakevalve timings. For example, intake valve opening time for cylindernumber one is indicated by dotted bar 561. The intake valves forcylinder number one are closed when no dotted bar is present above thecylinder strokes of cylinder number one. The intake valve opening timesfor the other cylinders are indicated at 563, 565, 566, 568, 569, 571,573, 576, and 579.

The engine noise observed in a knock window of one cylinder may includenoise related to events associated with other engine cylinders. Forexample, the engine knock window of cylinder number two indicated at 504may occur at a time when the knock sensor is exposed to noise from theDI injection to cylinder number four at 513 and this linkage is shownvia arrow 593. The relations between DI injections to other cylindersand the knock sensor output in other knock windows are illustrated viaarrows 590-597. Thus, the engine knock background noise level determinedfor the engine knock window of cylinder number two shown at 504 mayinclude noise generated by the DI injector opening and/or closing at513. In addition, the intake valve closing of cylinder number fiveindicated by dotted bar 573 show that the intake valve of cylindernumber five closes and may generate noise within the time that the knockwindow of cylinder number two is open as shown by bar 504. Further, theexhaust valve closing of cylinder number eight indicated by dotted bar578 shows that the exhaust valve of cylinder number eight closes and maygenerate noise within the time that the knock window of cylinder numbertwo is open as shown by bar 504. Further still, the exhaust valveopening of cylinder number seven indicated by bar 564 shows that theexhaust valve of cylinder number seven opens and may generate noisewithin the time that the knock window of cylinder number two is open asshown by bar 504. Thus, in this example, engine background noise asdetermined via the engine knock window for cylinder number two at 504may include noise from DI event 513, valve event 573, valve event 564,and valve event 578.

The poppet valve and DI injection times shown in FIG. 5 may beindicative of base DI and poppet valve timings. These timings may affectthe engine background noise levels determined from engine knock windowsof the cylinders (e.g., 504). While it may be desirable to include allbackground noise sources to determine a background noise level for aparticular cylinder, it may also be useful to decompose a totalbackground noise level into the contributions from individual noisesources. By removing one or more noise influences from a total enginebackground noise level, it may be possible to determine engine noiselevels that may be used to determine whether or not knock is present inother cylinders. For example, a base engine knock background noise levelfor cylinder number one may be used as a base engine knock backgroundnoise level for cylinder number three. Further, the poppet valve noiseor DI injector noise of one cylinder may be applied to a differentcylinder to estimate engine knock background noise for the differentcylinder. Such allocations of engine knock background noise levels maybe useful when an engine knock background noise level has not beenobserved for a particular engine cylinder or if opportunities forlearning engine knock background noise levels is limited by vehicleoperating conditions. Output of a knock sensor may be sampled (e.g.,measured) via the controller and processed when a knock window is openas shown at windows 501-508.

Referring now to FIG. 6, a timing sequence 600 that illustrates one wayof changing a knock sensor that is sampled during a cylinder's knockwindow is shown. The illustrated timings are for an eight cylinderengine that has a firing order of 1-3-7-2-6-5-4-8. The engine is a fourstroke engine that has a cycle of 720 crankshaft degrees. The enginecrankshaft degrees are located along the horizontal axis and zerodegrees represents top-dead-center compression stroke for cylindernumber one. The eight cylinders are labeled along the vertical axis.

The fuel injections, valve timings, cylinder strokes, and engineposition for each of the cylinders shown in FIG. 6 are identical tothose shown in FIG. 5, except as noted below. Therefore, for the sake ofbrevity, the description of these items will not be repeated.Nevertheless, the timings and sequence shown in FIG. 6 is identical tothat shown in FIG. 5, except as noted.

In this example, output of knock sensor 90 a is sampled or measured viathe controller during the knock windows of cylinder numbers three andfour. Thus, knock windows for cylinder numbers three and four have beenrevised to 602 and 607 to indicate that output of a different knocksensor is sampled during the knock windows of cylinder numbers three andfour. In this example, the knock sensor that is sampled in the knockwindows of cylinder numbers three and four is switched when degradationof knock sensor 90 b is suspected.

Engine knock background noise levels for cylinder numbers three and fourmay also be relearned when output of one knock sensor sampled during theknock windows of cylinder numbers three and four is replaced by outputof a second knock sensor sampled during the knock windows of cylindernumbers three and four. In this way, the engine background noise levelfor cylinder numbers three and four may be adjusted according to outputof the knock sensor that is sampled during the knock windows of cylindernumbers three and four. This may improve detection of knock in cylindernumbers three and four. This sequence only shows changing from a primaryknock sensor to a secondary knock sensor for cylinder numbers three andfour, but knock sensors sampled in knock windows of other cylinders maybe changed in a similar way.

Referring now to FIG. 7, a timing sequence 700 that illustrates one wayof changing fuel injection timing to adjust engine knock backgroundnoise levels during a cylinder's knock window is shown. The illustratedtimings are for an eight cylinder engine that has a firing order of1-3-7-2-6-5-4-8. The engine is a four stroke engine that has a cycle of720 crankshaft degrees. The engine crankshaft degrees are located alongthe horizontal axis and zero degrees represents top-dead-centercompression stroke for cylinder number one. The eight cylinders arelabeled along the vertical axis.

The fuel injections, valve timings, cylinder strokes, and engineposition for each of the cylinders shown in FIG. 7 are identical tothose shown in FIG. 5, except as noted below. Therefore, for the sake ofbrevity, the description of these items will not be repeated.Nevertheless, the timings and sequence shown in FIG. 7 is identical tothat shown in FIG. 5, except as noted.

In this example, timing of direct fuel injections for cylinder numbersseven and five are adjusted to reduce an amount of engine knockbackground noise in the knock windows of cylinder numbers seven andeight. Specifically, timings of injections 712 and 717 are advanced sothat direct fuel injectors do not close during knock windows 503 and 508of cylinder numbers seven and eight. The fuel injector timings may beadjusted to increase the signal to noise ratio of knock sensor output sothat identification of engine knock may be improved.

Engine knock background noise levels for cylinder numbers seven and fivemay also be relearned when fuel injection timings (e.g., fuel injectoropening and closing times or crankshaft angles) are adjusted so thatidentification of engine knock accuracy may improve. In this way, theengine background noise level for cylinder numbers seven and five may beadjusted according to engine noise that may occur during the knockwindows of the cylinders. This may improve detection of knock incylinder numbers seven and five. This sequence only shows fuel injectoradjustments for two cylinders, but fuel injection of all enginecylinders, one engine cylinder, or other numbers of cylinders may beadjusted in a similar way.

Referring now to FIG. 8, a timing sequence 800 is shown that illustratesintake and exhaust valve closing timing adjustments that may be made toreduce engine knock background noise levels for engine cylinders. Thevalve timings may be adjusted to allow the determination of the totalcylinder background noise level for cylinder i at the present enginespeed and load Cyl_bkg_noise(i), the base cylinder background noiselevel that does not include noise from fuel injectors and/or intakeand/or exhaust poppet valves that open and/or close during a knockwindow of cylinder (i) Cyl_base_noise (i), the fuel injector noise thatoccurs during a knock window of cylinder (i) Cyl_inj_noise (i), and thenoise from intake/exhaust valves that open and/or close during a knockwindow of cylinder (i) Cyl_vlv_noise (i).

The fuel injections, valve timings, cylinder strokes, and engineposition for each of the cylinders shown in FIG. 8 are identical tothose shown in FIG. 5, except as noted below. Therefore, for the sake ofbrevity, the description of these items will not be repeated.Nevertheless, the timings and sequence shown in FIG. 8 is identical tothat shown in FIG. 5, except as noted.

The illustrated timings are for an eight cylinder engine that has afiring order of 1-3-7-2-6-5-4-8. The engine is a four stroke engine thathas a cycle of 720 crankshaft degrees. The engine crankshaft degrees arelocated along the horizontal axis and zero degrees representstop-dead-center compression stroke for cylinder number one. The eightcylinders are labeled along the vertical axis

Intake closing time adjustments may be made as shown at 802, 804, 806,808, 810, and 812 to lower the engine knock background noise levels thatmay be observed in knock windows 501, 502, 503, 504, and 506.Specifically, intake valve closing event times or crankshaft angles maybe adjusted so that the intake valves do not close when a knock windowis open. Further, exhaust closing time adjustments may be made as shownat 811, 813, 815, and 817 to lower the engine knock background noiselevels that may be observed in knock windows 505, 506, 507, and 508.Specifically, exhaust valve closing event times or crankshaft angles maybe adjusted so that the exhaust valves do not close when a knock windowis open. Of course, engine knock background noise of engine cylindersmay be increased via moving poppet valve closings into knock windows ofengine cylinders.

Engine knock background noise levels for the engine cylinders may alsobe relearned when poppet valve opening and closing timings are adjustedso that identification of engine knock accuracy may improve. In thisway, the engine background noise level for the engine cylinders may bereduced if engine knock background noise levels become larger as theengine ages. This may improve detection of knock in the enginecylinders.

Note that the example control and estimation routines included hereincan be used with various engine and/or vehicle system configurations.The control methods and routines disclosed herein may be stored asexecutable instructions in non-transitory memory and may be carried outby the control system including the controller in combination with thevarious sensors, actuators, and other engine hardware. The specificroutines described herein may represent one or more of any number ofprocessing strategies such as event-driven, interrupt-driven,multi-tasking, multi-threading, and the like. As such, various actions,operations, and/or functions illustrated may be performed in thesequence illustrated, in parallel, or in some cases omitted. Likewise,the order of processing is not necessarily required to achieve thefeatures and advantages of the example examples described herein, but isprovided for ease of illustration and description. One or more of theillustrated actions, operations and/or functions may be repeatedlyperformed depending on the particular strategy being used. Further, thedescribed actions, operations and/or functions may graphically representcode to be programmed into non-transitory memory of the computerreadable storage medium in the engine control system, where thedescribed actions are carried out by executing the instructions in asystem including the various engine hardware components in combinationwith the electronic controller.

It will be appreciated that the configurations and routines disclosedherein are exemplary in nature, and that these specific examples are notto be considered in a limiting sense, because numerous variations arepossible. For example, the above technology can be applied to V-6, I-4,I-6, V-12, opposed 4, and other engine types. The subject matter of thepresent disclosure includes all novel and non-obvious combinations andsub-combinations of the various systems and configurations, and otherfeatures, functions, and/or properties disclosed herein.

The following claims particularly point out certain combinations andsub-combinations regarded as novel and non-obvious. These claims mayrefer to “an” element or “a first” element or the equivalent thereof.Such claims should be understood to include incorporation of one or moresuch elements, neither requiring nor excluding two or more suchelements. Other combinations and sub-combinations of the disclosedfeatures, functions, elements, and/or properties may be claimed throughamendment of the present claims or through presentation of new claims inthis or a related application. Such claims, whether broader, narrower,equal, or different in scope to the original claims, also are regardedas included within the subject matter of the present disclosure.

1-7. (canceled)
 8. An engine operating method, comprising: sampling output of a knock sensor in a knock window of a selected cylinder via a controller; and adjusting poppet valve timing in response to less than a threshold total number of engine knock indications being generated from sampling of the knock sensor in the knock window of the selected cylinder.
 9. The method of claim 8, further comprising adjusting fuel injection timing in response to less than the threshold number of knock indications being generated from sampling of the knock sensor in the knock window of the selected cylinder.
 10. The method of claim 9, where the adjusting the fuel injection timing includes moving a closing time of a fuel injector from a timing inside the knock window to a timing outside of the knock window.
 11. The method of claim 9, further comprising learning an engine knock background noise level after adjusting the poppet valve timing.
 12. The method of claim 9, further comprising learning an engine knock background noise level after adjusting the fuel injection timing.
 13. The method of claim 8, where the adjusting the poppet valve timing includes moving a closing time of a poppet valve from a timing inside the knock window to a timing outside of the knock window.
 14. The method of claim 8, where the knock window is an angular range of a crankshaft where output of the knock sensor is sampled.
 15. A system for operating an engine, comprising: an engine including at least one vibration sensing engine knock sensor; and a controller including executable instructions stored in non-transitory memory to adjust poppet valve timing of the engine via the controller in response to a request to learn one or more engine knock background noise levels.
 16. The system of claim 15, further comprising additional instructions to adjust fuel injector timing in response to the request to learn one or more engine knock background noise levels.
 17. The system of claim 15, where the request to learn one or more engine knock background noise levels is based on a distance traveled by a vehicle.
 18. The system of claim 15, where the request to learn one or more engine knock background noise levels is based on an amount of time the engine has operated since manufacturing of the engine.
 19. The system of claim 18, further comprising additional instructions to adjust a cylinder firing pattern in response to the request to learn one or more engine knock background noise levels.
 20. The system of claim 15, further comprising additional instructions to adjust a cylinder firing density in response to the request to learn one or more engine knock background noise levels.
 21. The system of claim 15, where the at least one vibration sensing engine knock sensor includes a first knock sensor and a second knock sensor, and further comprising: additional instructions to sample output of the first knock sensor in a knock window of a selected cylinder; and additional instructions to sample output of the second knock sensor in the knock window of the selected cylinder in response to generating less than a threshold total number of engine knock indications from sampling of the first knock sensor in the knock window of the selected cylinder.
 22. The system of claim 21, where the first knock sensor is positioned physically closer to the selected cylinder than the second knock sensor, and where the output of the first knock sensor is not sampled in the knock window when the output of the second knock sensor is sampled in the knock window.
 23. The system of claim 15, further comprising additional instructions to adjust poppet valve timing of the engine in response to less than a threshold total number of engine knock indications being generated from sampling of the at least one vibration sensing knock sensor in a knock window of a selected cylinder.
 24. The method of claim 23, further comprising additional instructions to adjust fuel injection timing of the engine in response to less than the threshold number of knock indications being generated from sampling of the at least one vibration sensing knock sensor in the knock window of the selected cylinder. 